Glutamate neurotoxicity has been implicated as an important pathogenetic mechanism in the central nervous system, and appears to play a critical role in causing the neuronal death that occurs in stroke. The mechanisms whereby glutamate kills neurons are unknown. Astrocytes appear to protect neurons against glutamate neurotoxicity both in vivo and in vitro. This project has the long-range goal of trying to further our understanding of how glutamate kills neurons, how astrocytes may protect neurons against glutamate toxicity, and how disturbances of astrocyte function might contribute to glutamate toxicity. Previous work by the P.I. and others has demonstrated a crucial role for glutamate uptake in protecting neurons from glutamate toxicity. In addition, the P.I. has shown that under conditions of reduced uptake, as in cortical cultures with few astrocytes present, neurons are exquisitely sensitive to glutamate toxicity. Recent work by others has shown that the glutamate transporter may actually operate in reverse, under certain circumstances. Therefore failure of the transporter would be disastrous for neurons, since even a small rise in extracellular glutamate would be expected to be toxic to neurons. The model system for this work will be rat embryonic cerebral cortex in dissociated cell culture. The specific aims of this project are to: 1) use selective culturing to characterize the astrocyte and neuronal glutamate uptake systems; 2) determine whether pharmacological blockade of glutamate uptake significantly alters the sensitivity of neurons to glutamate in astrocyte-rich and in astrocyte-poor cultures; 3) determine whether failure of glutamate uptake can be demonstrated in cortical cultures. The specific hypothesis to be tested in this research is that the glutamate transport system in astrocytes is important in protecting neurons from glutamate toxicity. Disruption of astrocyte function leading to an impairment of glutamate uptake and reversal of transport may be the critical events in the pathogenesis of glutamate toxicity in vivo.